(1) Field of the Invention
The invention is related to an emergency opening system of an aircraft cabin door with the features of the preamble of claim 1.
(2) Description of Related Art
Aircraft doors fulfill the following major functions: They provide access for the passengers and for the crew to the aircraft cabin and allow the evacuation of the aircraft cabin in an emergency case. Additionally the doors also carry, unfold and inflate a slide used to evacuate the passengers from the aircraft in case of an emergency. EASA CS 25.807 differs between different types of emergency exits for passenger aircrafts with regard to capacity of passengers.
For type A doors a maximum of 110 passengers are allowed and for type B doors 75 passengers are allowed (FAR 25.807). Within a given evacuation time of 90 seconds the given number of passengers/crew members shall be able to leave the aircraft. For this purpose typical aircraft doors are designed in such a way that the door opening—including inflation of the slide—is performed in not more than 10 seconds. Different means of power assisted opening devices are used to allow a rapid door opening. Basically a translational or a rotary power opening device can be used. The majority of all aircraft doors use a pneumatic axial cylinder as a working element and a pressure pot as energy storage. Alternatively a mechanical spring can be used as energy storage and a simple linear slide can be used as a working element. Rotary systems use a condenser as energy storage and an electric drive. Alternatively gas motor systems are known which use an explosive as energy storage.
A ‘Pneumatic Actuator’ system is used to assist the rapid door opening and to provide enough force to drop the slide from its packed position on the door. State-of-the-art aircraft doors follow the principle of initial inward movement. The basic opening motion (swivel) is provided by the coupling-curve of a four-joint-gear. The gear is realized by two levers (parallel lever and hinge arm) and the door leaf as linkage. Typically the pneumatic actuator is located parallel to one lever of the four-joint-gear. Another mechanical element is used to transfer its axial force into the passenger door structure. The power actuator pushes the door from its unlocked, unlatched, lifted but closed position to its open position. The push-actuation mode creates discrete forces in the passenger door structure. Especially in case of a blockage during the power assisted opening the door structure has to carry discrete forces without damage. These discrete forces may be a problem for certain door system layouts, especially for door structures made from Carbon Fibre Reinforced Plastic (CFRP).
According to document DE 101 61 562 B4 existing aircraft doors use a pneumatic cylinder (working element) together with a pressure pot (energy storage). A door latching requires a z-movement of a door leaf of an aircraft cabin door. A mechanical element is connected in a rotatable way to the cabin door as well as to the power opening. Since the distance to this element changes during the lift motion the mechanical element is realized as telescopic rod used to compensate the door z-movement during its opening cycle and to introduce the actuator forces into the door leaf. The door leaf distributes the forces to different bearing points.
One bearing point is the pivot point of the parallel levers in the top of the door. The other bearing point is the mechanical connection of the connecting links to the door. The working element is positioned parallel to the hinge arm as a lever of a so-called “four-joint-gear”. This arrangement creates the following load path: The source of the force is the actuator which changes the pressure energy into an axial force. This force will be applied to a telescopic rod and acts on the door leaf.
The actuator load acting on the door leaf creates a load path via the connecting links and the hinge arm back to the origin of the force. A major disadvantage of this system is the introduction of a discrete load into the door leaf, especially a discrete load with a z-component if the door is closed and the actuator is under power, i. e. a typical case of misuse. A further disadvantage is the length of the load path, the usage of the telescopic rod system and the application of the z-load-component. Especially in a CFRP door the local introduction of a high force causes the need for local reinforcements. These reinforcements are typically made from titanium and create high cost and extra weight.
The coupling of the swivel and the lift system and the application of a telescopic rod create another major disadvantage with respect to the basic kinematic system. Generally the system is in a non-defined status as a movement in the telescopic rod can be initiated by the lift or the swivel motion or a mix of both. The system is defined if preconditions, such as extra boundary conditions are fulfilled. Such preconditions are as follows: the telescopic rod is fully compressed and blocked by a physical stop; the telescopic rod is fully extended and blocked by a physical stop. In order to make the intermediate condition between compressed and extended condition predictable a spring unit is required.
The disadvantage based on the fact that the system status is generally non-defined is that the system design process is complex and requests iterative loops to deliver a properly working unit. In addition it is known from previous designs that the non-defined status is also critical at the end of a door emergency opening motion. Before the door reaches its end position the system needs to be decelerated. The non-defined nominal status, caused by the spring loaded telescopic rod, complicates the controlled deceleration of the door, i. e. damping device.
Alternatively to a pressure pot mechanical springs are used as energy storage and a linear slide provides the axial force at the place of a pneumatic cylinder as working element. A major disadvantage is the ‘energy density’ in the mechanical springs. If the springs are made from metal the system is not competitive in comparison to the existing solutions. If the system uses CFRP spring elements the technical challenge is even higher and evidence is required that no creeping effect will decrease the single spring force during the lifetime of the pneumatic actuator system.
The document DE 102 58 105 B4 discloses a rotary electric motor system, i. e. a motor+constant gear, arranged in such a way that any acting torsion moment is created by an electrical engine and applied directly in the rotation axis of the system. The passenger door uses a four-joint-gear as basic swivel kinematics. The drive for this kinematic system is provided by the electrical engine. This engine includes the constant gear to adjust the force as well as the opening time. The motor applies its opening moment directly into the rotational axis (main rotation axis) of the system so that the door is no longer pushed to open but is rotated to open. This rotary electric motor system has been developed for a day to day application of a big and heavy door, i. e. the door movement is power assisted at any time.
In case of an emergency opening the power level is increased so that the full door movement is achieved by the system. There are consequences for this rotary electric motor system with regard to durability and the weight of the energy storage as well as with regard to the reactive-moments. Since all the opening torque is provided by only one axis again a situation of local load concentration comes into existence. In the end heavy and costly brackets are required to react the torsion moment. In addition to that the motor-gear unit consumes a lot of volume in a volume-sensitive area of the door-system.
The document DE 10 2008 014 691 A1 discloses a rotary gas motor system together with an explosive. Instead of a condenser the system is powered by an explosive. The explosive material reacts relatively slowly so that energy in the form of expanding gas volume is produced over the opening time. The expanding gas is transferred via a gas engine and a gear into a torsion moment. The gas motor is arranged so that the torsion moment acts directly on the rotation axis of the swivel system. The gas motor systems also suffer from the limited available space as well as from reacting torsion moments. The acceptance by airliners and/or by passengers of explosives in an aircraft cabin has to be seen as critical. In addition to that it is known from other industries that the spare-logistics for explosive material are difficult and costly.
The document U.S. Pat. No. 5,379,971 shows a chain system which is powered by a pneumatic linear actuator. The system combines the pneumatic linear working element with a rotary opening of the door. The chain system shows advantages from the point of load introduction. The torsion moment is applied symmetrically via two axes. But the chain system in total uses a high number of single parts and thus it is heavy, expensive and difficult to maintain.
The document DE 4022067 C2 proposes to use a rotary motor system external from the door system which is accommodated in the airframe. To open an air cabin door from outside the airframe may be seen as advantageous form a product side. But from a technical administration point of view a high number of internal interfaces are created. These interfaces are difficult to manage before the systems reach an acceptable level of performance. In addition to that it is known from previous aircraft developments that the available space in the area of the door surrounding is also extremely limited.
The object of the invention is to provide an emergency opening system for an aircraft cabin door that avoids or reduces discrete forces to an aircraft cabin door as a result from power assisted door opening.